Hybrid silica membranes for oxy-fuel conversion membrane reactors

The growing energy demand combined with increasing concerns about greenhouse gas emissions is driving the research towards the development of processes with integrated CO2 capture. The present research aims at the development of ceramic membranes for use in a reactor concept, enabling hydrogen production with integrated CO2 capture, commonly referred to as pre-combustion carbon capture.

The research is focused on the design of a water gas shift membrane reactor (WGS-MR). In this reactor, the syngas feed that will come from an autothermal reformer (ATR) will be converted to hydrogen and CO2 by means of the water gas shift reaction.

This reaction is slightly exothermic (ΔH = -41.16 kJ/mol), therefore hydrogen will be removed from the reactor by means of a hydrogen selective membrane to ensure a high conversion of CO.

Membranes that are utilized in a WGS-MR need to have a high hydrogen permeance and a high H2/CO2 selectivity, but most important is that they should be hydrothermally stable. Hybrid silica membranes based on 1,2-bis(triethoxysilyl)ethane (BTESE) have an excellent hydrothermal stability but do not have the required selectivity.

In this research metal dopants are used to tune the separation performance of the BTESE membranes in order to increase the H2/CO2 selectivity, while keeping the hydrogen permeance as high as possible.

Scanning electron micrograph of a metal doped hybrid silica membrane. From left to right: macroporous α-Al2O3 support layer, mesoporous γ-Al2O3 intermediate layer of 3 μm and a microporous hybrid silica layer of 220 nm.